To extend our discovery that ovarian steroids serve as endocrine control signals in regulating the amount of oxytocin released in response to vaginal distention stimuli, we will examine the possibility that this control may be significant in labor and related processes such as abortion. To do this, we will measure the responsiveness of the vaginal distention reflex and the rates of production of progesterone and prostaglandin F sub 2 alpha while simulating endocrine events of labor in sheep bearing utero-ovarian transplants. Although not widely exploited in studies of the endocrinology of parturition, this animal model should serve well in such investigations. Progesterone exerts its influence on the reflexive release of oxytocin at a site in the brain. By pursuing preliminary findings indicating that biogenic amines and prostaglandins of central origin seem to influence oxytocin secretion, we hope to establish a basis for testing the proposition that one or more of these substances may be involved in progesterone's mechanism of action. By systematically assessing the effects of intracarotid and intracerebroventricular administration of monoamines, monoamine precursors, prostaglandins and inhibitors of the synthesis of these compounds on the vaginal distention reflex, knowledge of the roles of the substances in the operation of the reflex should emerge. Steps can then be taken to see if progesterone acts on the reflex by influencing the synthesis, release or mode of action of any of these substances in the CNS.